The group B streptococci (GBS) are major perinatal pathogens. Our long-term objectives are to develop immunologic approaches to the management of these infections, either by active or passive immunization or with antibodies used therapeutically. More than one approach may be appropriate. Our laboratory has begun to develop sensitive, quantitative assays for antibodies, the native type-specific capsular polysaccharides of GBS. Enzyme-linked immunosorbent assays (ELISA) have been completed for IgG antibody to GBS Ia and GBS Ib. We are now proceeding to isolate the native antigen and develop the ELISAs for antibody to GBS II and GBS III. We have also published an indirect fluorescent antibody (IF) test, which is simpler to perform and compares well with ELISA, but is only semiquantitative and less sensitive. In order to determine what concentration of antibody is necessary for protection in newborn infants, we are measuring the levels of human IgG antibody to the type-specific antigens of each serotype in passively immunized mice, which are required for protection against experimental infection with homologous and heterologous strains of GBS. We are studying maternal-cord serum pairs of full-term and premature infants to determine the kinetics of transplacental passage of antibody. We are determining the concentration of antibody to the native antigens in cord blood or maternal sera of infected infants. The levels of antibody to GBS types Ia and Ib in infected infants are below the protective levels in mice, but more clinical data are needed to support the current estimates of protective levels to GBS Ia and Ib, and animal data are needed for GBS II and III. We will obtain data on the prevalence of antibody measured by ELISA in the parturient woman and examine the effect of age, race, socioeconomic status, and colonization with GBS on the prevalence of antibody in these subjects. We will attempt to develop a quantitative assay for IgM antibody to GBS type III, compare its protective activity with IgG antibody in the mouse, and obtain data on the development of IgM and IgG antibody to GBS III during infancy to determine whether IgM antidoby may explain the age-specific attack rates of GBS disease. These studies will result in tests that will allow clinicians to assess the level of antibody to GBS in the sera of pregnant women and to predict whether the newborn infant will be susceptible to infection. They will provide methods for evaluating the efficacy of GBS vaccines and the development of immune serum globulin if and when active immunization is not possible. They should yield new information on the specificity of antibody in relation to function.